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Paint Viscosity

03/11/2017 12:58 PM

Dear All

I want to know whether industrial paint viscosity increases with time. Recently I came across one incident that epoxy paint is of manufacturing year 2012. we used paint in 2017. Paint coverage whichis normally 6-8 sqmts/litre but in this case coverage was only 2.41 sqmts/lit. What can be the reason is it viscosity of some thing else.

Re: Paint viscosity

03/11/2017 5:52 PM

Remember, epoxy paint is a curing paint. As made with solvent it has a shelf life, even mixed. AFter application the solvent evaporates and the anti curing agent (also called driers) evaporates and the paint cures to its final hardness. Your paint, even with driers, has partially cured = more viscous = thicker coat = fewer square meters per liter

Re: Paint viscosity

03/12/2017 9:35 AM

Sorry i did not got your point. I am saying that paint lying unused in sealed cans for about 4-5 yearsand it opened in 2017. Then does solvent and anti curing agent evaporates during unused time of 5 years or does it evaporates immediately after opening cover or evaporates gradually after opening. Please guide me.
Regards
Pradeep

Re: Paint viscosity

03/12/2017 10:17 AM

Epoxy paint is metastable - it is ready to cross link, but the stabilizing additives and cross linking additives(driers) holg curing at bay, however random collisions allow for a slow degree of curing to take place - this results in a suggested shelf life of ~~1 tear(this varies with whoever made it). This gradual curing means the paint gradually gets more viscous = thicker coating - as you experienced. You can offset this by adding a little more of the suggested thinner for this paint to reach the application viscosity as measured by a draining cone/cup or other method

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Re: Paint viscosity

03/11/2017 7:15 PM

I work with coatings on a professional basis. Every coating I buy is good for 1 year. You used a coating that is 5 years old, chances are that the main thinning component, has evaporated. You are lucky that your only problem is the coverage.

It's called a shelf life. All coatings have one.

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Re: Paint viscosity

03/11/2017 7:59 PM

Another component that effects coverage is the substrate that the paint is applied to, wood, metal, concrete, gypsum board (drywall) etc, the more absorbent = less coverage. With 5 yr old epoxy paint I'm surprised you were still able to use it, damn self-life

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Re: Paint viscosity

03/11/2017 10:41 PM

We always store cans, with friction fit lids, that contain volatile products upside down. This promotes less evaporation of the volatile compounds since the heavier compounds better seal the lid. I haven't looked lately but the famous 'Plastic Wood" filler was being produced with the label 'upside down' to encourage inverted storage...and it works!

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